Ice grader having vertical rotary cutters



Sept 15, 1964 R, E. THoMPsoN 3,148,917

ICE GRADER HAVING VERTICAL ROTARY CUTTERS Filed May l0. 1961 5Sheets-Sheer 1 www \llllll/ N l) 0 0 0 0 0 0 0 *l cvag viator/295 Sept15, 1954 R. E. THOMPSON 3,148,917

ICE GRADER HAVING VERTICAL ROTARY CUTTERS Filed May 1o. 1961 3SheelZs--Sheeii 2 (Joa #wor/235 Sept. 15, 1964 R. E. THOMPSON ICE GRADERHAVING VERTICAL ROTARY CUTTERS 5 Sheets-Sheen 3 Filed May l0, 1961 i 4 ll n INVENToR. ,@os/ ZZ/OMPso/U Jafar/aga 2W BY United States Patent O3,148,917 ICE GRADER HAViNG VERTICAL RTARY CU'E'IERS Roy E. Thompson,Los Angeles, Calif., assigner to Western Gear Corporation, Lynwood,Calif., a corporation of Washington Filed May 10, 1961, Ser. No. 109,1196 Claims. (Ci. 299-25) This invention deals generally with gradingequipment and, particularly, with an ice grading machine.

Airelds, especially military airfields, are now located in the far-Hungcorners of the globe. The main requisite of an airfield, of course, isthat it have smooth runways for take-off, landing, and taxiing.

In airfield locations of extreme cold, such as the Arctic, an ice eld isconveniently leveled and smoothed to form runways. These runways must beperiodically cleared of snow and resurfaced to maintain them in theproper condition. An ice field may be leveled for purposes other thanmaking a runway, of course. The leveled ice area may serve as afoundation for a building structure, for example, or as a storage area.

Insofar as I am aware, existing ice graders utilize a forward,horizontal, rotating ice cutter. This cutter is supported at its ends inbearings which are carried on supporting arms extending forwardly of theice grading vehicle. Such supporting arms limit the maximum depth ofpenetration of the cutter into the ice to less than the cutting radiusof the cutter. In many instances, this cutting radius is not suicient toachieve a properly leveled ice surface. For example, it may benecessary, to attain such a properly leveled ice surface, to cut througha solid wall of ice which may have a height exceeding the cutting radiusof the horizontally disposed rotary ice cutter and possibly evenapproaching the diameter of the rotary cutter. The existing ice graders,with their outboard supporting arms for the rotary cutter, cannotpenetrate such a solid wall of ice because of the interference betweenthese arms and the side walls of the cut made in the ice by the cutter.With the existing ice grading equipment it is also diiicult to attain auniform cutting depth.

It will be appreciated that during operation of an ice grader, a largeramount of ice chip debris is created by the action of the rotary cutter.In the existing ice graders of which I am aware, there is no provisionfor removing this debris continuously from the vicinity of the cutter.The necessity of removing the debris, however, is not too critical withthe horizontal rotary ice cutter. In the present ice grader, on theother hand, anrappreciably greater amount of debris is created whichmust be continuously removed during an ice grading operation.

A general object of the present invention is to provide anice gradingmachine which avoids the above noted and other deficiencies of existingice graders.

Another object of the invention is to provide an ice grading machinewhich is capable of an appreciably greater depth of cut than theexisting ice grading machines and which can perform ice gradingoperations of which the existing grading machines are incapable, such aspenetrating solid walls of ice.

Another object of the invention is to provide an ice grading machinewhich accurately maintains a uniform cutting depth.

Another object of the invention is to provide an ice grading machine ofthe character described having provision for removal of the ice chipdebris produced by the machine in operation.

Other objects, advantages, and features of the invention will becomeevident as the description proceeds.

Briey, the objects of the invention are attained by 3,148,9i'? PatentedSept. l5., 1964 providing an ice grading machine equipped with a vehiclefor moving over the ice Vtield to be graded and at least one andpreferably three vertical, rotary ice cutters ahead of the forward endof the vehicle. These cutters are supported at their upper ends on avehicle supported frame so that the permitted cutting depth attainedwith the machine is limited only by the axial length of the cutters. Arelatively deep cutting depth is thereby attained.

When three rotary cutters are employed, one is located ahead of theother two and approximately on the longitudinal center line of themachine so that they cut a continuous wide path through the ice. Thecutters are rotated in such a way that they tend to direct ice chipsinto the space between the three cutters. This ice chip debris iscontinuously removed from this space and delivered to the rear end ofthe vehicle, from whence it may be discharged into a truck fortransportation to a suitable point of disposal, by a unique conveyorwhich extends along the underside of the vehicle. The forward end ofthis conveyor mounts a skid on which the rotary cutters of the machineare supported. In this way, an accurately uniform cutting depth isattained.

When the rotary ice cutters of the machine are cutting through a body ofice, the rotary cutters are subjected to numerous torsional impacts. Forthis reason, the present ice grading machine embodies a unique torsionaldrive for each rotary cutter, which drive absorbs the torsional impacts.

A better understanding of the invention may be had from the followingdetailed description thereof, taken in connection with the annexeddrawings, wherein:

FIG. 1 is a view in perspective of a presently preferred embodiment ofthe present ice grading machine;

FIG. 2 is a top plan view of the ice grading machine of FIG. 1 onreduced scale and with the tractor of FIG. l shown in phantom lines forclarity;

FIG. 3 is a side elevation of the structure shown in FIG. 2;

FIG. 4 is an enlarged section taken along line 4 4 of FIG. 3;

FIG. 5 is an enlarged section taken along line 5 5 of FIG. 4;

FIG. 6 is an enlarged section taken along line 6 6 of FIG. 4; and

FIG. 7 is an enlarged section taken along line 7 7 of FIG. 4.

Referring rst to FIG. 1, and speaking generally, the illustrated icegrading machine comprises a mobile support shown as a vehicle 10 onwhich is mounted a vertically swingable frame 12. Rotatably mounted onthe forward end of this frame, ahead of the vehicle 10 and with theiraxes of rotation vertical, are three rotary icc cutters 14 and 16.

The cutters 14 and 16 are driven from an engine 18 at the end of thevehicle in such directions that they tend to throw ice chips or debrisinto the space between the rotors. The debris is continuously carriedfrom the cutters to the rear of the Vehicle by conveyor 20. A rear,upwardly inclined conveyor 22 receives the debris from the conveyor 20and discharges it into a truck 100 for transportation to a suitabledisposal point. The forward end of the conveyor 2i) serves as a skid onwhich the forward end of the frame 12 is supported to attain accuratecontrol of the cutting depth of the cutters 14 and 16.

The ice grading machine will now be described in great-er detail.Vehicle 1t) has been illustrated as comprising a self-propelled vehicle,namely, a Caterpillar tractor. It will become evident as the descriptionproceeds, however, that the vehicle may be a specially designed,self-pr-opelled vehicle rather than a conventional dieser? vehicle, suchas a Caterpillar tractor. ln the alternative, the vehicle may consist ofa towed vehicle with wheels or skids.

Frame 12 is a generally open, rectangular structure which includeslongitudinally extending arms 24. The rear ends of lthese arms arepivotally connected to the ends of a cross member 26 which is rigidlyattached to the tractor frame by means of braces 2S. Frame 12 is therebyvertically swingable on the tractor vehicle 19.

At the forward ends of the arms 24, frame 12 comprises a hollow,supporting part 30. This part has a generally equi-lateral, triangularconfiguration and is rigidly attached, at two of its base apices, to theforward ends of the frame arms 24.

Referring to FiG. 5, part 3d will be seen to comprise a hollow,open-topped part 32, to the upper edges of the side walls of which isbolted a cover plate 34. Also, as shown best in FIG. 5, ice cutter 14comprises a hollow, cylindrical drum 36. Extending across the inside ofthe drum is a circular ange 33. Flange 3S has a central hole in which isfixed a lbearing 40. Rigidly attached within the drum 36, adjacent itslower end, is a ring 42 to which is joined, by a conical wall 44, asecond bearing 46.

Bearings 40 and 46 are rotatably fitted on a vertical, hollow supportingshaft 48. The upper end of this shaft extends through the lower wall ofthe supporting part 30 and is welded or otherwise rigidly joinedthereto. Braces 50 may be placed, as shown, to lend rigidity to thesupporting shaft 43. The reason why the supporting shaft 48 must be sorigid will become evident as the description proceeds. Fixed to thesupporting shaft 48, above the upper drum bearing dil and below thelower drum bearing 46, are thrust bearings 52 which restrain the drumagainst axial movement on the supporting shaft.

A centrally bored plate 54 is fixed to the lower side of the drum ring42. Extending through the central opening in the plate 54, and keyed tothe latter, is the lower end of a drive shaft S6. The upper end of thisdrive shaft is keyed to a relatively large gear 58 which is rotatablymounted on the upper end of the supporting shaft;Y 4S.

From this description, it lis evident that ywhen the gear 5S is driven,the rotary cutter 14 is driven in rotation through the drive shaft S6. Astudy of FG. 5 will show that the drive shaft 56 is quite slender, inVcomparison to the diameter of the cutter, for example, and has beeneven shown as being reduced in diameter to enhance the slenderness ofthe drive shaft. Drive shaft 56 is thus proportioned so that it willform a torsionally elastic connection between the gear 58 and thecutter. This torsional elasticity of the drive shaft is necessary toabsorb the torsional impacts which occur on the cutter in operation.

The cutting action of cutter 14 is furnished by a mul-tiplicity ofspikes 60 fixed to and extending outwardly from the cylindrical wall ofthe drum 36. Fixed to the lower end of the drum 36 are downwardly andoutwardly inclined spikes 62. During operation of the machine, thespikes 60 cut through the ice wall confronting the cutter, while thelower spikes 62 perform not only this function but the additionalfunction of facing or smoothing the yhorizontal ice surface exposed bythe cutter.

As may be best observed in FIGS. 2 and 4, cutters 14 and 16 are locatedat the apices of an equilateral triangle. Cutter 14 is located ahead ofcutters 16 and approximately on the center line of the vehicle 10.Behind the cutter 14 are the two cutters 16 which are located atopposite sides of that center line. Cutters 16 are substantiallyidentical and are rotatably mounted -on the supporting part 30 of theframe 12 in precisely the same way as described inV connection withcutter 14 and illustrated in FIG. 5. For this reason, it is notnecessary to describe further these cutters 16 or their manner ofsupport on the supporting part 30. Actually, the upper cutter 16 in FIG.4 is identical to cutter 14, while the lower cutter 16 in FIG. 4 isidentical with cutter 14 except that the spikes 66 on the latter cutter16 extend in the opposite tangential direction from those on the cutter14.

It will be observed that the center distance of each cutter 16 from thecenter line C is slightly -less than the sum of the cutting radii of theforward cutter 14 and the respective cutter 16. In this way, the threecutters are arranged to cut a continuous swath or path through the ice.It is obvious, of course, that lthe cutting diameters of the cuttersmust be such that the width of this path is somewhat greater than thewidth of the vehicle 1t) to permit the latter to travel in the path.

To theV upper ends of the drive shafts 56 of the two rear cutters 16 arefixed large gears 5S (FIG. 2) like that on the drive shaft of cutter 14.The gears 58 on the drive shafts of cutter 14 and the upper cutter 16will be seen to be drivably coupled by an idler gear 64. Idler gear 64is rotatably mounted within the supporting part 36 in any convenientway. From this description, it is evident that cutter 14 and the uppercutter 16 in FiG. 2 rotate in the same direction.

The cutters 14 and 16 are driven as follows: Within the rear supportingmember 26 is a rotary drive shaft 66. This shaft is driven from theengine 13. At its ends, shaft 66 mounts bevel gears 68. T hese bevelgears mesh with bevel gears 76 on the rear ends of two long,longitudinally extending drive shafts 72 within the frame arms 24. Attheir forward ends, shafts 72 are drivably connected to the two cutters16 by means of gearing 74, stub shafts 76, and meshing bevel gears 78and 86 on the stub shafts 76 and the drive shafts 56 of cutters 16. Asshown in FIG. 4, the forward cutter 14 and the upper rear cutter 16 inthat figure are driven in counterclockwise directions of rotation, asthe cuters are viewed in FIG. 4. The lower rear cutter is driven in aclockwise direction of rotation.

Because of their directions of rotation, the rotary ice cutters 14 and16 tend to throw ice chips into the space between the cutters, whichchips would rapidly accumulate and produce a large quantity of debrisbetween the rotors if the debris were not continuously removed during anice surfacing operation. For this reason, the present ice gradingmachine is provided with conveyors 29 and 22 for removing the debris. Asshown best in FlGS. 2, 3, 4, 6 and 7, conveyor 20 comprises a longconduit or frame member 82 on the longitudinal center line of thevehicle. This frame member is formed with two upwardly open channels ortroughs 84. The forward end of the frame member 82 extends into thespace between the ice cutters 14 and 16. The side walls 36 of thetroughs 84 terminate some distance from this forward end of the framemember. Accordingly, at the forward end of the member, the troughs 84are laterally open to permit the ice debris to enter the forward ends ofthe troughs 84.

Within each trough 84 is a helical conveyor S8. These conveyors arerotatably mounted at 'their forward and rear ends in bearings 90. Attheir rear ends, the helical conveyors 88 are driven from the cutterdrive shaft 66 through a chain drive generally denoted by the numeral92. The helical conveyors are driven in the directions of rotationindicated in FIG. 7 to feed the ice debris entering the forward ends ofthe troughs 84 along the troughs to the rear ends of the latter.

The rear conveyor bearings 90 (only one shown) are located some distancefrom the rear ends of the troughs 84. The lower end of the rear,inclined conveyor 22 is located below the rear ends of the troughs 84.In this Way, the ice debris carried along the troughs by the helicalconveyors 88 is discharged onto the lower end of the conveyor 22.Conveyor 22 comprises an endless conveyor member 94 having cross ribs96. A chain drive 98 driven from the cutter drive shaft 66 drives theendless conveyor member 94 in the direction indicated in FIG. 3.Accordingly, the ice debris discharged onto the conveyor member 94 bythe helical conveyors 8S is carried upwardly to the upper end of theconveyor member 22 from whence the debris drops into a truck 100. Thistruck travels along with the ice grader and, when lled, transports thedebris to a sui-'table disposal point.

It will be observed in FIGS. 2 and 3 that the engine 18 is supported ontwo longitudinal frame members 102 which are welded or otherwise rigidlyattached at their forward ends to the cross member 26 and are pinned orotherwise attached at their rear ends to the rear conveyor 22. Framemembers 162, then, support the conveyor 22 in its inclined position.

At the forward end of the longitudinal conveyor frame member 82, thecenter rib 104 of the member is enlarged and projects some distanceabove the edges of the trough side walls 86 and the center rib 104, asindicated at 1%. The bottom wall 108 of the troughs S4 curves up andaround the forward end of this enlarged rib portion 106 to form a skid11G. During operation oft the grading machine, this skid rides on thesurfaced ice behind the forward rotary ice cutter 14. Fixed to the upperedge of the enlarged rib portion 106 is a plate 112. Rotatably connectedat its lower end to this plate is a jackscrew 114. Jackscrew 114 extendsupwardly through the supporting part 30 of the hinged frame 12 andpasses through an axially fixed, rotary nut 116 driven by a motor 11S.Motor 118 is controllable from the cab of .the Vehicle 10.

From this description, it is evident that the hinged frame part 3i), andthe rotary ice cutters 14 and 16 carried thereon, are supported on theskid 11i). By controlling the motor 11S, the frame part 30 and icecutters 14 and 16 may be raised and lowered. The pulpose of thisadjustment is to achieve a uniform cutting depth. Such a uniform cuttingdepth is attained when the lower cutter spikes 62 are coplanar with thelower surface of the skid 110. Hence, the adjustment alforded by thelead screw 114.

In operation of the present ice grading machine, the vehicle is operatedto move the rotary ice cutters 14 and 16 over the ice surface to beleveled. It is obvious that the vertical disposition of the ice cuttersenables the latter to penetrate any ice wall having a height not greaterthan the length of the cutters. This penetration depth is obviouslyappreciably greater than that of which horizontally mounted ice cuttersare capable. As the cutters cut through the ice, the debris thrown intothe space between the cutters is continuously carried away and depositedin a truck 160 by the conveyors 20l and 22. While in the illustrativeembodiment, the ice debris is deposited in a truck for transportation toa suitable disposal point, the debris might be expelled or thrown to theside of the machine by a suitable blower or the like.

As the cutters 14 and 16 move over the ice, the lower spikes 62 smoothoff the horizontal ice surface exposed by the cutting action of thecutters. The cutters are raised or lowered, as required, by operation ofthe motor 118 to place the lower ends of the lower cutter spikes 62 incoplanar relationship to the lower surface of the skid 11i) so as toassure maintenance of a constant cutting depth. As mentioned earlier,the torsionally elastic drive shafts 56 for the rotary cutters absorbsthe torsional impacts which are produced on the rotary cutters inoperation.

Clearly, then, the invention hereinbefore described and illustrated isfully capable of attaining the several objects and advantagespreliminarily set forth. While a presently preferred embodiment of theinvention has been described and illustrated, numerous modifications inthe design, arrangement of parts, and instrumentalities of the inventionare obviously possible within the spirit and scope of the followingclaims.

What is claimed is:

1. A grading machine, comprising a mobile support having upper and undersides and front and rear ends, a. frame extending longitudinally of saidsupport adjacent the upper side thereof, means pivotally connecting therear end of said frame to said support for vertical swinging movement ofthe frame relative to the support, the forward end of said frameextending forwardly of the forward end of said support, a plurality ofrotary cutters arranged below said forward end of said frame with theiraxes of rotation generally vertical, means rotatably mounting saidcutters on said forward end of said frame, means for driving saidcutters in rotation, a member extending longitudinally of said supportadjacent the under side thereof, means pivotally connecting the rear endof said member to said support for vertical swinging movement of themember relative to the support, the forward end of said member extendingforwardly of the forward end of said support, a skid on the forward endof said member for engaging a surface to be graded, means supportingsaid forward end of said frame on said forward end of said member withthe lower ends of said cutters disposed at the approximate level of theunder surface of said skid for engagement with the surface to be graded,and said cuters being offset laterally of said support to cut a pathalong said surface at least as wide as said support.

2. The subject matter of claim 1 wherein said frame extends along theupper side of said support to the rear end of the support and the frameis pivotally connected to the latter end of the support, and said memberextends along the under side of said support =to the rear end of thesupport and is pivotally connected to the latter end of the support.

3. A grading machine, comprising a mobile support having upper and undersides and front and lrear ends, a frame extending longitudinally of saidsupport adjacent the upper side thereof, means mounting said frame onsaid support, the forward end of said frame extending forwardly of theforward end of said support, three rotary cutters arranged below saidforward end of said frame with their axes vertical and with their lowerends coplanarly disposed for engagement with a surface to be graded, oneof said cutters being located approximately on the longitudinal centerline of said support and the remaining two cutters being locatedrearwardly of said one cutter and at opposite sides of said center lineso as to cut a path along said surface at least as wide as said support,a conduit extending longitudinally of said support along the under sidethereof approximately on said center line, means mounting said Conduiton said support, the forward end of said conduit being located betweenand having lateral `openings facing said remaining cutters, the loweredges of said openings being located at the approximate level of thelower ends of said cutters, means for driving said cutters in rotationin such manner that the forward side of each of said remaining cuttersrotates toward said center line, whereby rotation of said cutters tendsto discharge material removed from the surface being graded into theforward end of said conduit through said openings therein, conveyormeans in said conduit for conveying the material entering the conduitrearwardly through the latter, and the rear end of said conduit beingopen and located at the rear end of said support.

4. The subject matter of claim 3 wherein said conveyor means compriserotary helical conveyor means extending longitudinally through saidconduit.

5. The subject matter of claim 3 wherein the interior of said conduit isdivided by a vertical, longitudinally extending wall, and said conveyormeans comprises a pair of rotary helical conveyor members extendinglongitudinally through the conduit at opposite sides of said wall.

6. The subject matter of claim 3 wherein said frame mounting meanscomprises means pivotally connecting the rear end of said frame to saidsupport for vertical swinging movement of the frame relative to thesupport and said conduit mounting means comprises means pivotallyconnecting the rear end of said conduit to said support for verticalswinging movement of the conduit 7 relative to the support, the forwardend of said conduit having an under skid surface at the approximatelevel of the lower ends of said cutters, and means supporting theforward end of said frame on the forward end of said conduit.

References Cited in the le of this patent UNITED STATES PATENTS 721,697Hanneborg Mar. 3, 1903 1,615,461 Lichtenberg Jan. 25, 1927 2,066,207Lestina Dec. 29, 1936 8 Hargrove et al. Apr. 16, 1940 Lewis May 6, 1952Hui Dec. 7, 1954 Newcomer July 5, 1955 Kozub Oct. 20, 1959 Wilcox Ian.10, 1961 Aibley Sept. 4, 1962 FOREIGN PATENTS Australia Sept. 4, 1958Germany July 11, 1957

1. A GRADING MACHINE, COMPRISING A MOBILE SUPPORT HAVING UPPER AND UNDERSIDES AND FRONT AND REAR ENDS, A FRAME EXTENDING LONGITUDINALLY OF SAIDSUPPORT ADJACENT THE UPPER SIDE THEREOF, MEANS PIVOTALLY CONNECTING THEREAR END OF SAID FRAME TO SAID SUPPORT FOR VERTICAL SWINGING MOVEMENT OFTHE FRAME RELATIVE TO THE SUPPORT, THE FORWARD END OF SAID FRAMEEXTENDING FORWARDLY OF THE FORWARD END OF SAID SUPPORT, A PLURALITY OFROTARY CUTTERS ARRANGED BELOW SAID FORWARD END OF SAID FRAME WITH THEIRAXES OF ROTATION GENERALLY VERTICAL, MEANS ROTATABLY MOUNTING SAIDCUTTERS ON SAID FORWARD END OF SAID FRAME, MEANS FOR DRIVING SAIDCUTTERS IN ROTATION, A MEMBER EXTENDING LONGITUDINALLY OF SAID SUPPORTADJACENT THE UNDER SIDE THEREOF, MEANS PIVOTALLY CONNECTING THE REAR ENDOF SAID MEMBER TO SAID SUPPORT FOR VERTICAL SWINGING MOVEMENT OF THEMEMBER RELATIVE TO THE SUPPORT, THE FORWARD END OF SAID MEMBER EXTENDINGFORWARDLY OF THE FORWARD END OF SAID SUPPORT, A SKID ON THE FORWARD ENDOF SAID MEMBER FOR ENGAGING A SURFACE TO BE GRADED, MEANS SUPPORTINGSAID FORWARD END OF SAID FRAME ON SAID FORWARD END OF SAID MEMBER WITHTHE LOWER ENDS OF SAID CUTTERS DISPOSED AT THE APPROXIMATE LEVEL OF THEUNDER SURFACE OF SAID SKID FOR ENGAGEMENT WITH THE SURFACE TO BE GRADED,AND SAID CUTERS BEING OFFSET LATERALLY OF SAID SUPPORT TO CUT A PATHALONG SAID SURFACE AT LEAST AS WIDE AS SAID SUPPORT.
 3. A GRADINGMACHINE, COMPRISING A MOBILE SUPPORT HAVING UPPER AND UNDER SIDES ANDFRONT AND REAR ENDS, A FRAME EXTENDING LONGITUDINALLY OF SAID SUPPORTADJACENT THE UPPER SIDE THEREOF, MEANS MOUNTING SAID FRAME ON SAIDSUPPORT, THE FORWARD END OF SAID FRAME EXTENDING FORWARDLY OF THEFORWARD END OF SAID SUPPORT, THREE ROTARY CUTTERS ARRANGED BELOW SAIDFORWARD END OF SAID FRAME WITH THEIR AXES VERTICAL AND WITH THEIR LOWERENDS COPLANARLY DISPOSED FOR ENGAGEMENT WITH A SURFACE TO BE GRADED, ONEOF SAID CUTTERS BEING LOCATED APPROXIMATELY ON THE LONGITUDINAL CENTERLINE OF SAID SUPPORT AND THE REMAINING TWO CUTTERS BEING LOCATEDREARWARDLY OF SAID ONE CUTTER AND AT OPPOSITE SIDES OF SAID CENTER LINESO AS TO CUT A PATH ALONG SAID SURFACE AT LEAST AS WIDE AS SAID SUPPORT,A CONDUIT EXTENDING LONGITUDINALLY OF SAID SUPPORT ALONG THE UNDER SIDETHEREOF APPROXIMATELY ON SAID CENTER LINE, MEANS MOUNTING SAID CONDUITON SAID SUPPORT, THE FORWARD END OF SAID CONDUIT BEING LOCATED BETWEENAND HAVING LATERAL OPENINGS FACING SAID REMAINING CUTTERS, THE LOWEREDGES OF SAID OPENINGS BEING LOCATED AT THE APPROXIMATE LEVEL OF THELOWER ENDS OF SAID CUTTERS, MEANS FOR DRIVING SAID CUTTERS IN ROTATIONIN SUCH MANNER THAT THE FORWARD SIDE OF EACH OF SAID REMAINING CUTTERSROTATES TOWARD SAID CENTER LINE, WHEREBY ROTATION OF SAID CUTTERS TENDSTO DISCHARGE MATERIAL REMOVED FROM THE SURFACE BEING GRADED INTO THEFORWARD END OF SAID CONDUIT THROUGH SAID OPENINGS THEREIN, CONVEYORMEANS IN SAID CONDUIT FOR CONVEYING THE MATERIAL ENTERING THE CONDUITREARWARDLY THROUGH THE LATTER, AND THE REAR END OF SAID CONDUIT BEINGOPEN AND LOCATED AT THE REAR END OF SAID SUPPORT.